The sonication of an aqueous solution of TlCl3 under a flow of argon has led to a precipitate, which is composed of two products. The major product is Tl2OCl2, while Tl2O is obtained in small quantities. The later has a structure of a multi-shell closed compound. The identification of the inorganic fullerenes in the TEM picture as the thallium(I) oxide is based on SAED measurements.

A New Fullerene-like Inorganic Compound Fabricated by the Sonolysis of an Aqueous Solution of TlCl3

The activity behavior of carbon monoxide and propene oxidation on Cu Cr catalysts was investigated by varying both the catalyst composition and the heat-treatment conditions. γ-Alumina supported CuO, Cr 2 O 3 and Cu Cr oxide catalysts were employed. The Cu Cr catalysts were treated by heating at 300–900°C under oxidizing or reducing atmosphere. Calcined at 700–900°C under oxidizing atmosphere, the formation of Cu 2 Cr 2 O 4 spinel structure resulted in an enhanced activity not only for carbon monoxide oxidation but also for propene oxidation. On the other hand, treatment in a reducing atmosphere at 700–900°C produced a sintered copper surface but induced a strong metal-support interaction that led to an enhancement in activity, but only for carbon monoxide oxidation. Additionally, the synergistic effect resulting from the ligand effect, as Cr 2 O 3 species is closely associated with CuO species, occurs for carbon monoxide oxidation. The activity of propene oxidation on the CuO catalyst reaches a maximum at a copper content of about 10 wt.-% and that on the Cr 2 O 3 catalyst reaches a maximum at a chromium content of about 25 wt.-%.

Effect of heat-treatment conditions on CuCrγ-alumina catalyst for carbon monoxide and propene oxidation

The electrical conductivity, σ, and thermoelectric power, S, of copper chromite (CuCr2O4) are reported in the temperature range 295 to 815 K A break (TB) in the slope of the plot of log σ against T−1 was observed around 556 K Apart from this break, the curves are linear, and their slopes correspond to activation energies of 060 eV (TB 556 K) A break (T′B) in the slope of the -S against T−1 plot was also observed round 556 K Apart from the break at this temperature, the S against T−1 curves are linear At T′B>556, S can be expressed by the relation 

$$S = - \left[ {\left( {\frac{{065 eV}}{{{\text{2}}eT}}} \right) + (042) mV K^{ - {\text{1}}} } \right]$$

The mechanism involved in the electrical transport is the hopping of holes from Cr4+ centres to neighbouring Cr3+ ions The typical hopping mobility of the holes is of the order of 106 m2 V−1 sec−1 The mobility activation energy of the holes in CuCr2O4 decreases with temperature due to the smoothing of the potential barriers between Cr4+ and Cr3+ sites

Electrical transport in copper chromite catalyst

Enhanced performance of barium and cobalt doped spinel CuCr2O4 as decomposition catalyst for ammonium perchlorate

Different coloured thallous tungstates were prepared by solid state reaction between thallous carbonate and tungsten trioxide at higher temperatures. The structure and thermal stability of different thallous tungstates were determined by powder X-ray diffraction and thermogravimetric analysis, respectively. The electrical conductivity (σ) and thermoelectric power (5) of pressed solid pellets of Tl2WO4 are reported in the temperature range 295 to 950 K. It is concluded that these materials have large numbers of oxygen ion vacancies and conduction occurs due to the electrons left by oxygen ions while escaping the solid. These electrons are trapped in the valence band and form centres analogous to a helium atom and electrical conductivity results when they enter the conduction band. The values of donor ionization energies have also been evaluated.

Structure, thermal stability and electrical transport in coloured thallous tungstates

Solid thallous carbonate reacts with chlorine gas with the formation of brown-coloured Tl2OCl2 as an intermediate compound. Further exposure to chlorine gas gives the yellow compound Tl4Cl6. Both the compounds contain Tl(I) and Tl(III) ions. The kinetic data obeyw2=kt. The energy of activation was found to be 41.98 kcal mol−1. Thermo-gravimetry (TG) indicates that Tl2OCl2 decomposes into TlCl, Tl2O3 and chlorine gas above 250° C. In contrast, Tl4Cl6 is stable up to 420° C.

Solid-state chemistry of new Tl2OCl2 and Tl4Cl6

Electrical conductivity, σ, Seebeck coefficient, S, measurements on the pressed solid pellets of both Tl2OCl2 and Tl4Cl6 have been carried out in the temperature range 300 to 580 K. Both log a and S against T−1 plots have two linear regions with a break at temperature TB and T′B for both solids. T′B has been found to few degrees less than TB, which has been shown due to the experimental condition employed in the measurement of σ and S. These solids are electronic conductors with relatively high conductivity. The conduction above TB, results due to thermal excitation of electrons from valence to conduction band. The energy band gap for Tl2OCl2 and Tl4Cl6 have been found to be 1.38 and 1.68 eV, respectively. Below TB, the hopping of electrons from Tl+1 to Tl+3 becomes the dominant conduction mechanism. The estimated values of mobility in this range for both the solids are of the order of 10−6 m2 V −1sec−1.

Electrical transport in new Tl2OCl2 and Tl4Cl6

The electrical conductivity (σ) and thermoelectric power (S) for the system La1−xNdxTlO3 (0 ⩽x⩽ 1.0) in the temperature range 295 to 805 K are reported. Both logσ andS as a function ofT have been found to be linear with a break in the slope around a specific temperature,TB. The break temperature systematically decreases as we proceed from the systemx=0 tox=1.0. It has been concluded that conduction belowTB is extrinsic and takes place owing to hopping of electrons localized on the defect centre Tl2+ to Tl3+ on normal sites. Conduction aboveTB is the normal band type in all systems. The energy band gap has been evaluated in all cases and it has been found that it decreases systematically fromx=0 tox=1.0.

P. N. Ojha

Papers

Solid-state chemistry of new Tl2OCl2 and Tl4Cl6

Electrical transport in new Tl2OCl2 and Tl4Cl6

Electrical transport in copper chromite catalyst

Structure, thermal stability and electrical transport in coloured thallous tungstates

Electrical transport in new La1−xNdxTlO3 (0≤x≤1) system